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  1. #271
    Photo Engineer's Avatar
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    I believe that Ian and I both have a lot to contribute to APUG. It is unfortunate that sometimes we misunderstand each other or disagree. I place no significance on these situations and merely try to pass on what I believe to be correct, based on the literature and my long experience.

    PE

  2. #272

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    Quote Originally Posted by Photo Engineer View Post
    Alan;

    Again, you misunderstand. In the diffusion of ions through gelatin, Hydrogen is the fastest and Hydroxide is second in rate, therefore you have an inrush of Hydrogen meeting Hydroxide and a wavefront of neutral water forming as the Hydrogen diffuses downward and Hydroxide moves upwards. When the wavefront reaches the bottom of the coating (or in our tests the undercoat with indicator dye), you stop the reaction. This is virtually instantaneous.

    There is a tiny gradient in charge which appears to be taken up by a shift in the equilibrium of the overall medium. Diffusion of Sodium and Acetate for example take place at only a slightly lower rate due to size and this is partly overcome by both shifts in equlibria and in the slight charge imbalance (if any) which takes place. Overall, in the average coating, all diffusion is done in about 15" or less, but the neutralization appears to take place in less than 5".

    The two major researchers at Kodak on this were Liang and Tong. They developed a diffusion model for water, hydroxide, acid, dyes and other chemicals through emulsions.

    One experiment had the acid anion and proton anchored in place through polymerization of the anionic portion of the acid molecule. They then showed the rapid diffusion of hydroxide into the acid layer to neutralize the alkali. Or, conversely, the proton (hydrogen ion) diffused upwards into the alkaline medium. This led to the development of proper barrier layers in instant products BTW and showed how diffusion and neutralization took place in coatings when acid and base were both present. This "timing layer" was crucial due to the rapid diffusion of either Hydrogen ion or Hydroxide ion. They had to be held back from each other while the development took place and the dyes diffused.

    PE
    OK. Let me be sure I understand what it is that you are suggesting. Once that is crystal clear then we can discuss the implications.

    What I thought I understood you to say is that hydrogen ions move from the solution into the emulsion in a fast inrush by process of diffusion. While this very fast process is occurring the other ions don't move much because their diffusion coefficients are much less than the diffusion coefficient of hydrogen ions. Then the other ions diffuse more slowly until everything is equilibrated. It is as if the hydrogen ions are running, and the other ions are walking, so the hydrogen ions leave the others far behind.

    In this scheme hydroxide ions are a partial exception to this description. They also undergo a fast diffusion, but not as fast as hydrogen ions, and these two types of ions diffuse in opposite directions.

    Along the way, as the inrushing hydrogen ions meet the outrushing hydroxide ions these two species combine to form water molecules.

    Is this a fair description of what you are saying?

  3. #273
    Photo Engineer's Avatar
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    Yes, it is so, but an approximation. It takes place over less than 15" at 68 deg F.

    PE.

  4. #274

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    Quote Originally Posted by Photo Engineer View Post
    A stop is not recommended with paper!
    PE
    Was that a typo?
    (post #126)

    Anyway guys,
    this topic has been beaten to a pulp!

    Nothing much to learn here
    (other than the unpublished Kodak science from PE' s noggin).

    Ian keeps saying water is OK,
    but seems IMHO to interpret Kodak etc. as saying they are equivelant
    PE on the otherhand clearly feels they are saying they are unequal
    but acceptable options.

    Is this such a hard concept to reconcile?

    Water is OK. It is not IDEAL. It is NOT ideal because there is less of a safety margin....

    Stops are preferable. They are not absolutely necessary.
    In fact, they are ideal... but usually not absolutely necessary.
    Last edited by Ray Rogers; 07-22-2010 at 11:03 PM. Click to view previous post history.

  5. #275
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    Sometimes Ian just goes on the warpath and won't listen to anything but what he wants to hear. It can be maddening at times.

    Anyways I use stop-bath with films. I even reuse it. Never had any issues. No pinholes, none of that paranoid nonsense.
    Stop worrying about grain, resolution, sharpness, and everything else that doesn't have a damn thing to do with substance.

    http://www.flickr.com/kediwah

  6. #276

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    Quote Originally Posted by Photo Engineer View Post
    Yes, it is so, but an approximation. It takes place over less than 15" at 68 deg F.

    PE.
    I think the best approach now for our sub-discussion is to take it in a series of small steps to best avoid misunderstandings or confusion.

    Let us set up a coordinate system to help clarify the discussion. Let the solution be on the left and the emulsion on the right.

    One implication of the model you have posed, together with the coordinate system defined above is the following. There is a net displacement of charge to the right. In other words, the emulsion is a slab of material that acquires a net positive charge because positively charged hydrogen ions have been transported into the emulsion. This leaves a net negative charge in the solution, most of which will be in a relatively thin layer near the solution-emulsion interface.

    A related effect occurs with the hydroxide ion, though to a lesser degree. They diffuse from the emulsion toward the solution. This is because the the concentration of hydroxide ions is higher in the emulsion than in the solution. This process adds to the net positive charge in the emulsion, i.e. removing negative ions (hydroxide ions) from the emulsion increases the net positive charge in the emulsion.

    We will consider the other ions to be relatively fixed in space because they diffuse much slower than hydrogen ions (and hydroxide ions.) This is of course an approximation.

    With respect to the reaction between hydrogen ions and hydroxide ions, this has no effect on the local net charge balance. This is the result of charge conservation. For example, let us consider a single hydrogen ion (do you mind if I just call them protons?) in close proximity to a single hydroxide ion. Considering only these two ions and not any other ions that may be in the vicinity, the net charge of the proton-hydroxide pair is zero. If these two ions then react to form a water molecule there is no change in the net local charge. Therefore, with respect to the location of the charge distributions there is no need to consider the acid-base neutralization reaction. (There could be an indirect effect because the neutralization reaction may change the concentration gradients, which in turn can affect the diffusion rates, but this is a fine point that need not concern us at this point.)

    Let us see if we can agree that this description is a consequence of the model you have proposed.

  7. #277

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    By the way, I am going on a business trip starting Friday morning, so I might be able to engage this conversation only intermittently for the coming week.

  8. #278

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    Quote Originally Posted by Ray Rogers View Post
    Ian keeps saying water is OK,
    but seems IMHO to interpret Kodak etc. as saying they are equivelant
    PE on the otherhand clearly feels they are saying they are unequal
    but acceptable options.

    Is this such a hard concept to reconcile?

    Water is OK. It is not IDEAL. It is NOT ideal because there is less of a safety margin....

    Stops are preferable. They are not absolutely necessary.
    In fact, they are ideal... but usually not absolutely necessary.
    Thought about it, and yes: i'm sure it's impossible to reconcile.
    It is possible to accept that there is a conflict between both views though. But reconcile, i don't think so.

    I mean, you too haven't managed to, but have chosen a side instead.


    And that (choose a side) is the only thing we can do, i guess.

  9. #279
    M.A.Longmore's Avatar
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    I think the best way to summarize this debate can be found here :
    http://www.youtube.com/watch?v=7IU1bzZheWk

    Enjoy The Weekend


    Ron

    From The Long Island Of New York, and the
    Long Island @ Large Format Group, right here on APUG
    .

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    Sanjay Sen - APUG Subscriber
    Sanjay Sen, 36, a champion of human and animal rights, died June 3 in a motorcycle accident in Wayne, New Jersey.

    July 23 1975 - June 3 2012

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  10. #280
    Ian Grant's Avatar
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    Quote Originally Posted by Ray Rogers View Post

    Ian keeps saying water is OK,
    but seems IMHO to interpret Kodak etc. as saying they are equivelant
    PE on the otherhand clearly feels they are saying they are unequal
    but acceptable options.

    Is this such a hard concept to reconcile?

    Water is OK. It is not IDEAL. It is NOT ideal because there is less of a safety margin....

    Stops are preferable. They are not absolutely necessary.
    In fact, they are ideal... but usually not absolutely necessary.

    Ray, I've never thought that they are equivalent overall because there are advantages in terms of fixer life, stopping development faster, but it does appear from Mason's comment that a stop bath or rinse is "Superfluous" that we are all giving the stop or rinse far more importance than is required. Fuji don't use either for mechanical processing of B&W films that says rather a lot.

    But yes I do think they are close enough equivalents in terms of the overall processing of films and Mason and others are quite clear about that. there's no evidence of any effects on image quality and the long term stability of the films.

    I totally agree with your comments, which you've summed up well, I'd add:


    Ilford -Stop bath is preferable. They are not absolutely necessary (with films).
    Kodak - very clearly say you can use either (with films) - which I find slightly odd as I'd have thought they would have taken the same line as Ilford


    Quote Originally Posted by Photo Engineer View Post
    I believe that Ian and I both have a lot to contribute to APUG. It is unfortunate that sometimes we misunderstand each other or disagree. I place no significance on these situations and merely try to pass on what I believe to be correct, based on the literature and my long experience.
    PE

    Just to put the record straight Ron, PE, is disagreeing with what Kodak & Ilford recommend, that you can use water instead of a stop bath with films which is part of the OP's question.

    Neither of us disagree with the fact that a stop bath will lengthen the life of a fixer, or stop development faster, I've said that in many posts in the thread. However talk of residual HQ is a smoke screen, particularly as the reference is to a Monobath which has rather different and more complex chemistry. With films a stop bath itself doesn't have time to remove all residual developing agent in the emulsion, so we need to be looking at the fixer and wash to help complete that.

    As I've said before it's that simple - YOU CAN USE A WATER RINSE with film, safely. If Ron disagrees he should take that up with Kodak it's been a recommendation since Mees joined the company nearly 100 years ago.

    __________________________________________________ __________________________________________________ _________
    This is Kodak's recommendations (again).

    FINAL STEPS
    Rinse at 65 to 75°F (18 to 24°C) with agitation in KODAK
    Indicator Stop Bath or running water for 30 seconds.

    That's up to date Kodak information in the current Tmax data sheet, and in other film data sheets as well.


    So anyone who can't agree and reconcile those plain fact's needs to take up the argument with Kodak, not me. It's a simple yes/no answer whether you can use a water rinse instead of stop bath, and both Ilford & Kodak say yes.

    Ian
    Last edited by Ian Grant; 07-23-2010 at 02:09 AM. Click to view previous post history. Reason: add



 

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